Abstract
Fatigue crack formation and early growth is significantly influenced by microstructural attributes such as grain size and morphology. Although the crystallographic orientation is a primary indicator for fatigue cracking, the neighbourhood conformed by the first and second neighbour grains strongly affect the fatigue cracking driving force. Hence, two identical grains may result in different fatigue responses due to their interactions with their microstructural ensemble, which determines the fatigue variability. Naturally, macroscopic samples with millions of grains and thousands of competing microstructural neighbourhoods can effectively resemble a representative volume element in which fatigue failure may seem deterministic. However, when considering systems in which fatigue failure is controlled by hundreds or less of grains, fatigue failure is stochastic in nature and the samples are not a representative but a statistical volume. This work studies fatigue crack nucleation in micron-scale Ni beams that contain a few hundred grains. This work presents 3D crystal plasticity finite element models to compute stochastic distribution of fatigue indicator parameters that serve as proxies for crack nucleation in statistical volume elements. The integration of experiments with models provides a method to understand the irreversible deformation at the grain level that leads to fatigue cracking. Our results explain the role of grain morphology of crack nucleation distribution
Highlights
The past decade have seen developments in the manufacturing of miniaturised components
The results demonstrate the role of grain morphology on fatigue crack initiation and present good agreement with experiments
A total of 10 microstructure realisations were considered for each grain shape to compare the fatigue crack nucleation life, ܰே௨
Summary
The past decade have seen developments in the manufacturing of miniaturised components. Recent years have seen the development of microstructure-sensitive crystal plasticity computational methods [9, 10] to represent the fatigue response at the grain scale. These approaches characterise the fatigue damage driving force at the microstructure scale by means of Fatigue Indicator Parameters (FIPs) [10,11,12]. Castelluccio and Mcdowell [10, 16] employed a Fatemi-Socie parameter for each octahedral slip system as surrogate driving force for early crack initiation Their proposed FIP was implemented along a 3D crystal plasticity mesoscale model that was used to investigate microstructure variability on fatigue behaviour at the micro scale. The results demonstrate the role of grain morphology on fatigue crack initiation and present good agreement with experiments
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